There are an estimated 1.5 million manual wheelchair users (mWCUs) in the United States, and an estimated 200 million wheelchair users worldwide. Manual wheelchair users depend on their upper limbs for mobility and activities of daily living. However, up to 70% of manual wheelchair users report shoulder pain. Shoulder pain in mWCUs has been directly linked to further disability including difficulty performing activities of daily living, decreased physical activity, and reduced quality of life. Overall, any loss of upper limb function due to pain adversely impacts the independence and mobility of mWCUs. Thus, it is imperative to provide innovative technologies, therapies, and interventions to minimize shoulder pain.
Using a powered wheelchair takes away all strain on the shoulders and reduces shoulder pain. However, powered chairs are not a viable option for most wheelchair users, because they are expensive, heavy (i.e., too heavy to load into a car, requiring special vans and lifts), have limited use duration due to battery life, require frequent recharging, provide little flexibility for persons who are capable of manually propelling their own chair, are sometimes too wide to fit through doorways, and contribute to reduced physical fitness due to limited upper body movement. Additionally, there is often a negative stigma attached to the use of these devices among manual wheelchair users.
In order to address this large segment of the community that experiences difficulty pushing a wheelchair, various designs have been provided in the art. Examples include power assist wheelchairs, lever operated wheelchairs, and manually gear shifting wheelchairs. Push-rim activated power assist wheelchairs (PAPAWs) were one of the first technologies that addressed this need. They are similar to power wheelchairs, but batteries and motors in the wheel hubs assist the user to push his/her chair. These devices have been shown to significantly reduce the amount of energy used by an mWCU. However, PAPAWs are not ideal since they are heavy (e.g., 53 lbs of added weight) and more difficult to maneuver than a manual wheelchair, as they require two large electric motors and a battery. Also, the range of such devices is limited before the battery needs recharged. Further, these devices are quite expensive, e.g., more than an entry level powered chair, and the price does not include the cost of a wheelchair frame.
Lever operated wheelchairs are an innovative way to utilize a more ergonomic rowing motion from the wheelchair user. An example lever operated wheelchair is provided in an add-on device from Wijit Wheelchairs (Roseville, Calif.). Evaluation of these devices has shown that levers are a more comfortable method of propulsion, and they reduce the amount of work from the shoulders. However, these devices do not follow the concept of a traditional wheelchair design; that is, use of hand rims. Such wheelchairs accordingly require a relatively high learning curve to switch between forward and reverse propulsion. With an unintuitive method for current manual wheelchair users of braking and pushing in reverse, these devices have not had wide acceptance.
Magic Wheels (Seattle, Wash.) created a two-speed wheelchair add-on system in which the second gear is specifically catered for going uphill. In a clinical trial using this device, subjects experienced a significant reduction in the severity of shoulder pain. However, a limitation is that the user has to stop and manually shift into the other gear, e.g., physically turn a dial on the side of the wheel to shift. For many wheelchair users who have limited dexterity in their hands (e.g., due to spinal cord injury), it is physically impossible to turn this dial. Further, users have to be cognizant of when to shift, and thus individuals with cognitive deficits such as traumatic brain injury, dementia, etc., are unable to utilize such a device.